During the Civil War Mohun had drawn his sword for the king, acquiring the rank of major, and acquitting himself as a soldier with much distinction.

He was celebrated by Lord Rochester as the AEsopus of the stage; Nat Lee delighted in his acting, exclaiming: "O Mohun, Mohun, thou little man of mettle, if I should write a hundred plays, I'd write one for thy mouth!" And King Charles ventured to pun upon his name as badly as even a king might when he said of some representation: "Mohun (pronounce _Moon_) shone like a sun; Hart like the moon!" Charles Hart, the Cassio of the Vere Street Theatre, could boast descent from Shakespeare's sister Joan, and described himself as the poet's great-nephew.

He, too, fought for the king in the great Civil War, serving as a lieutenant of horse under Sir Thomas Dallison in Prince Rupert's regiment.

He had been apprenticed to Robinson the actor, and had played women's parts at the Blackfriars Theatre, winning special renown by his performance of the Duchess in Shirley's tragedy of "The Cardinal." As an actor Hart won extraordinary admiration; he soon took the lead of Burt, and from his physical gifts and graces was enabled even to surpass Mohun in popularity.

He introduced Nell Gwynne to the stage, and became one of the sharers in the management and profits of the theatrical company to which he was attached.
There was soon an ample supply of actresses, and a decline altogether in the demand for boy-performers of female characters.